The accuracy of precision pointing systems is often diminished by the inevitable presence of nonlinear drag torques resulting from rolling bearing friction and power/signal transfer cabling across rotary joints. These torques are difficult to characterize and impossible to predict analytically. Therefore, the preferred approach is to sense the torques to provide torque knowledge that can be utilized by a controls designer to compensate for the nonlinearities.
Sensing torque directly in the precision motion control of spacecraft science platforms is recognized as a sound approach to significantly improving pointing performance. However, previous torque-sensor designs are unacceptable for spacecraft science-platform articulation control because the resulting devices are too flexible and of low resolution and low bandwidth. Typical prior art designs utilize displacement sensors configured on a flexible structure. Most designs use strain gauges as the sensing element, which requires rather flexible structures to obtain usable output signals. Other sensing elements also suffer from flexibility and dynamic range limitations, or would require equipment too large or too complex to be incorporated practically.